Medium MCQ +4 / -1 PYQ · JEE Mains 2022

Let $y=y_{1}(x)$ and $y=y_{2}(x)$ be two distinct solutions of the differential equation $\frac{d y}{d x}=x+y$, with $y_{1}(0)=0$ and $y_{2}(0)=1$ respectively. Then, the number of points of intersection of $y=y_{1}(x)$ and $y=y_{2}(x)$ is

  1. A 0 Correct answer
  2. B 1
  3. C 2
  4. D 3

Solution

<p>${{dy} \over {dx}} = x + y$</p> <p>Let $x + y = t$</p> <p>$1 + {{dy} \over {dx}} = {{dt} \over {dx}}$</p> <p>${{dt} \over {dx}} - 1 = t \Rightarrow \int {{{dt} \over {t + 1}} = \int {dx} }$</p> <p>$\ln |t + 1| = x + C'$</p> <p>$|t + 1| = C{e^x}$</p> <p>$|x + y + 1| = C{e^x}$</p> <p>For ${y_1}(x),\,{y_1}(0) = 0 \Rightarrow C = 1$</p> <p>For ${y_2}(x),\,{y_2}(0) = 1 \Rightarrow C = 2$</p> <p>${y_1}(x)$ is given by $|x + y + 1| = {e^x}$</p> <p>${y_2}(x)$ is given by $|x + y + 1| = 2{e^x}$</p> <p>At point of intersection</p> <p>${e^x} = 2{e^x}$</p> <p>No solution</p> <p>So, there is no point of intersection of ${y_1}(x)$ and ${y_2}(x)$.</p>

About this question

Subject: Mathematics · Chapter: Differential Equations · Topic: Order and Degree

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